Many illnesses or conditions require a sustained effective serum level of medicaments or agents in vivo to provide the most effective prophylactic, therapeutic or diagnostic results. In the past, single doses of medicaments typically resulted in insufficiently long periods of effective serum levels.
Attempts to control and sustain medication levels have more recently included the use of many biodegradable substances, such as poly(lactide) or poly(lactide-co-glycolide) microparticles containing the medicament. The use of these microparticles provided an improvement in the release characteristics of medicaments by utilizing the inherent biodegradability of polymers to improve the release of medicaments and to provide a more even, controlled level of medication. However, in some cases, the duration of release is limited by in vivo degradation properties of the polymer. Therefore, a need exists to exert additional control over in vivo release kinetics to provide longer periods of fairly consistent medicament serum levels in vivo.